Thanks, I already took it apart and meticulously cleaned everything. I also stoned all the surfaces including the back plate and again cleaned everything. I did initially find that two of the top jaws were bolted to the wrong master jaws and I thought that most certainly was my problem, but alas, it was not.Sounds like jaws may be in horrible shape. Maybe you can work on the a little and get better results. Take the thing apart and clean the scroll. It may be full of ancient crap.
Thanks for sharing your perspective, Ross, I do appreciate it.I have a different perspective to this question.
First off, I don’t place any premium on having a “set true” chuck.
A good quality steel body chuck that is direct or has a mounting plate.
It it’s a matter of your work approach.
If starting with raw stock to make your part, if your process is properly laid out and executed the , if any, runout is a non factor.
It’s important that the jaw faces are parallel , so that the part is gripped full length of the jaw.
I was taught , when using a 3 jaw to finish the part in a single chucking if possible, even at the expense of overall speed.
If a recheck is required to finish the part , a better holding system should be considered.
Collets, soft jaws or a 4 jaw are just better , more repeatable
Shaft work should be finished between centers if possible.
Any 3 jaw you purchase, will almost immediately begin to degrade with any use, the trick is to not depend on it being accurate as to overall runout.
Primary lathe at work is fitted with a Shunk Rota G manual 250mm chuck. $7000+ , not offered as an “adjust true”.
Not a scroll chuck but rather a sliding plate setup ( more accurate , constant geometry) I still work with the idea of finishing in a single chucking. (Exception of part of facing)I use soft jaws when doing multiple repeat parts.
PBA’s are not what they were 15 years ago when I bought one for my 10EE, that was the best chuck I’ve used, no more.Current ones I believe are made in Slovakia (?) and marked Pratt Burnerd America. I have one and it's very nice and quite accurate. I think the one I linked to was made before that era as it is still marked Pratt Burnerd International.
Wasn't going to go here because telling people their machining practices are ... errr ... possibly less than ideal doesn't make one any friends. But yeah, have to agree with both of you above, the fixation over runout in a three jaw is very youtubey. Do it all in one chucking is what I learned fifty years ago and no, I ain't gonna learn to snivel about it being the chuck's fault when it's my own lack of skill That's not further eddication, that's just dumb."Woe is me..........my 3 jaw has runout". IT'S A 3 JAW! (LOL)
Most of the fixes you described for beater chucks is beyond my skill level. As far as Set-Tru chucks, yes, the main purpose is to have the ability to adjust each part within a few tenths. However, as with all my adjustable chucks that are in good condition, I can adjust the chuck to a point that it is within the stated tolerance for any diameter part I clamp and that is important to me. So, I guess in your words, my hard-on was large enough for me to pay the extra coin for a chuck that suits my needs. Your mileage may vary but replacing the chuck was what worked best for me.Good morning All:
When the problem is as the OP describes:
"After dialing it in on a specific diameter part, it will not repeat on the same part and is off by several thousandths or more."
I've found a common problem with old beater chucks is that the scroll has too much clearance on its post, and will move around when you tighten the chuck.
If you cannot grip the same piece consistently over and over within around 0.0005" of TIR after you've dialed it in once with the Set-Tru screws and using the same pinion over and over, that's the diagnosis I am most suspicious of.
Next in line is worn jaw slots that allow the jaws to cant sideways or rock, and lowest on the list is a worn scroll.
I say this because if the scroll always rotates back to the same point when you clamp your workpiece and if you've already dialed it in once, then only changes in either the scroll's position within the chuck body or changes in the jaws positions within the chuck body can account for the inconsistency you see.
This remains true regardless of whether the clamping faces of the jaws are perfect, whether the pinions are worn, or whether the scroll is worn.
So I'd pull the chuck apart and see how much clearance there is between the bore in the scroll and the post on which it rides.
Fixing either is not trivial, but it is possible with enough patience.
Next I'd check the jaw slots for clearance with the jaws...a thou or two will not make much difference but more than that will.
Last point...the whole idea of a Set-Tru chuck is that you adjust out the runout with every clamping, so you can get it within tenths without much effort.
So even if the chuck is not ideal, I'd live with it unless you have such a boner for a new one that you're willing to drop the coin.
Only you (our OP) can decide how big your hard-on actually is.
See, your kalamazoo chuck would be wasted on me because from the very first time I was taught to use a lathe, I was taught to never even try that stuff. And this was all before there were any imports, with who knows what brands (tho I am pretty sure the six-jaws were Buck) because we would never even consider just turning a part around and expecting the chuck to be perfect.Everyone is the first to bitch about imports taking everything over (especially in the market that they serve) but when they are sourcing an item, they are all about the cheapest, or at least cheap-er.
And this is why the old name brand chucks are done, and their name stamped on some import unit.
I don't think I've ever ground anything in a collet ... between-centers guy here. But I can actually see my parts without one of those funky enlarging visorsMy Lyndex collets can hold maybe a tenth or two...plenty good for turning but rougher than guts for grinding.